1. Field of the Invention
The present invention relates to a lens driving device for moving a lens in an optical-axis direction, and further relates to an imaging device and a small-sized electronics device using this lens driving device.
2. Description of the Related Art
Small-sized electronics devices are widely used. As to this kind of the electronics devices, there are a cell-phone, a PDA (Personal Digital Assistant) and so forth having a built-in imaging device for taking a subject image and obtaining digital image data. Since the small-sized electronics device carried around comprises the imaging device, shooting is easily performed at any time without carrying a digital still camera, a digital video camera or the like. Moreover, it is general that this kind of the small-sized electronics device preliminarily has a data communication function utilizing infrared rays and so forth. Thus, there is an advantage that it is possible to immediately transfer the taken image data to another cell-phone, a personal computer, etc.
In the meantime, the imaging device built in the small-sized electronics device has a much smaller size in comparison with a normal digital still camera. Therefore, components of a lens, a CCD sensor and so forth are greatly restricted in size. Due to this, an image function and quality of the obtained image data are insufficient. At present, the imaging device built in the small-sized electronics device is not used as an alternative device of the digital still camera.
In order to break this circumstance, in recent years, a high-pixel small CCD sensor and a high-contrast small lens are developed so that the quality of the image is rapidly improved. Moreover, for the purpose of enriching the image function, some of the published small-sized electronics devices comprise an automatic focus function and a zoom function, which are normally incorporated in the digital still camera.
The automatic focus function and the zoom function are carried out by moving a lens inside the imaging device in an optical-axis direction. The imaging device built in the small-sized electronics device preferably employs a hollow stepping motor for driving the lens. In the stepping motor, a cylindrical hollow rotor is rotated by supplying a pulse current to a stator surrounding the periphery of the hollow rotor. This hollow rotor surrounds a lens barrel holding the lens.
The respective components of the above imaging device are secured by an upper cover and a lower cover. Between inner surfaces of the respective covers and an outer surface of the hollow rotor, gaps are formed so that the hollow rotor smoothly rotates.
However, due to the gap, the hollow rotor jounces in a direction perpendicular to the optical axis. Thus, there arises a problem in that the stator and the hollow rotor coaxially disposed are decentered. If the hollow rotor is rotated in the decentered state, unbalance is caused regarding attractive force and repulsive force, and the hollow rotor is attracted to a side nearing the stator.
Thereupon, the hollow rotor comes into contact with the inner surfaces of the respective covers while rotating. Consequently, electric power consumption increases and abnormal noise is caused.